Polyethylene copolymers having pendant ester groups such as ethylene/vinyl acetate (EVA) are conventionally subjected to alkaline hydrolysis to form the alcohol. For example, EVA (with xylene to promote solubility) is reacted in alcoholic sodium or potassium hydroxide to form a material with multiple OH groups. It is possible to form double bonds by dehydrating the polyhydroxy compound with a strong dehydrating agent such as sulfuric acid. Otherwise, it is difficult to introduce unsaturation into a polyethylene backbone other than between the terminal carbon and the adjacent carbon (forming an alpha olefin).
It would be desirable for some applications to introduce olefinic bonds into a polymer that has sufficient hydrophilic groups to be water soluble or at least easily emulsified in water. Polymers such as ethylene/acrylic acid (EAA) have this property. It would be theoretically possible to treat a terpolymer of ethylene, vinyl acetate and acrylic acid with alcoholic sodium hydroxide and then dehydrate to introduce unsaturation. In practice, the presence of free, pendant carboxy groups causes rapid esterification between a carboxy group and a hydroxy group on the same or different chain, resulting in cross-linking and a rapid increase in viscosity. The present invention overcomes this obstacle by synthesizing polyunsaturated, polycarboxylated polyolefins by a direct method, thus forming novel compounds. The products differ from "alpha olefins" is having both double bonds and pendant carboxyl groups throughout the chain and not merely at the terminal carbon.
Copolymers of alkenes and 2-ene-carboxylic acids are known to have emulsifiability properties not present in polyalkenes. For example, copolymers of ethylene with acrylic acid, methacrylic acid or ethacrylic acid in minor amounts are easily emulsified in water. By 2-ene-carboxylic acids are meant the compounds of the formula ##STR1## The acids of particular interest are those where R.sub.1 is H or methyl or ethyl (respectively acrylic, methacrylic and ethacrylic). Higher acids could be used, but are not as common. These acids are also referred to as alpha-beta unsaturated acids. The alkenes or olefins involved usually include ethylene, propene, 1-butene, 2-butene and butadiene, with ethylene being the most common monomer.
Terpolymers of ethylene, an ester such as vinyl acetate and acrylic acid are disclosed in U.S. Pat. Nos. 3,215,678 and 3,909,280. U.S. Pat. No. 3,215,678 indicates that any vinyl ester of a 1-6 carbon, saturated, monobasic carboxylic acid may be used as the ester monomer, with the preferred esters being vinyl formate, vinyl propionate and the vinyl butyrates, and the most preferred ester being vinyl acetate: ##STR2## It should be appreciated that, after polymerization, each alkene monomer becomes ##STR3## with R.sub.2 and R.sub.3 each being H or methyl or ethyl (in the preferred polyethylene polymers, R.sub.2 and R.sub.3 are both H). Also after polymerization, each 2-ene-carboxylic acid monomer becomes ##STR4## wherein R.sub.1 is H or alkyl having 1-5 carbons. Also, after polymerization, each vinyl ester monomers becomes ##STR5## wherein R.sub.4 is H or alkyl having 1-5 carbons (preferably methyl or ethyl). Hereafter carbon-bonded hydrogens will be omitted. Thus the terpolymers of alkene 2-ene-carboxylic acid and vinyl ester have the formula ##STR6## wherein m, n and p are integers representing the relative proportions of the three monomers, with the monomers being arranged in substantially random order.
U.S. Pat. No. 3,215,678 discloses copolymers of ethylene with certain ester and acid comonomers. Briefly, a major portion of ethylene is copolymerized with at least 5% by weight of a vinyl ester of a lower (1-6 carbon) saturated monobasic aliphatic carboxylic acid and 0.01 to 10% by weight of acrylic or methacrylic acid, the balance consisting essentially of ethylene. A mixture of comonomers is copolymerized in the presence of a free-radical polymerization initiator such as a peroxygen compound, e.g., lauryl peroxide or t-butyl peracetate, or an azobis compound, e.g., azobisisobutyronitrile, at a somewhat elevated temperature, e.g., 90.degree.-250.degree. C. and at a pressure of 1000 to 1750 atmospheres. The polymer has melt indexes from 0.5 to 200 and generally 5 to 25, indicative of a high polymer molecular weight. The above patent is incorporated herein for a detailed description of the process and product.
U.S. Pat. No. 3,909,280 discloses ethylene/acrylic acid/vinyl acetate telomer waxes prepared by reacting 2 to 7 (preferably 3-4) mole % of acrylic acid and 0.5 to 8 (preferably 3-5) mole % of vinyl acetate, both based on ethylene, in the presence of a free radical initiator and a telogen. The mixture is reacted in the vapor phase of a suitable reactor at temperatures of from about 140.degree. C. to 200.degree. C. and pressures of from about 5,000 to 10,000 psi in known manner; and, once equilibrium is established, the product is continually withdrawn from the bottom of the reactor as it is formed. Free radical initiators, including peroxy and azo initiators are used in amounts of about 1.3.times.10.sup.-4 to about 4.times.10.sup.-4 mols of initiator per mol of monomer. A telogen is used (containing generally up to four carbons and up to two oxygens and being free of olefinic unsaturation) in amounts of about 12 to 28%, by weight of ethylene, preferably remaining relatively constant (.+-.1%) once equilibrium was established in the reactor. The above patent is incorporated herein for a detailed description of the process and product.